Conventionally, a rotating electric machine or a motor is used as a power source of a hybrid car, a pure electric vehicle, and so forth. A motor comprises a cylindrical stator core, coils wound around a plurality of teeth projecting inward in the diameter direction from the inner circumferential surface of the stator core, and a rotor rotatably held within the stator and having permanent magnets provided on, or in the vicinity of, the external circumferential surface thereof. With electricity fed to the coils, a magnetic field formed within the stator varies or shifts in the circumferential direction, whereby the rotor is driven to rotate.
With the above described motor activated, a current flows in the coils, which generates heat. This heat is transmitted from the teeth to the stator, causing iron loss, or the like. Further, an excessive current may flow temporarily or continuously into the coils, depending on the state of operation of the motor. This may possibly cause abnormal increase of temperature and damage the coils. Therefore, a motor usually has a temperature sensor, such as a thermistor, or the like, for detecting coil temperature, provided on a coil end portion so that a motor current is controlled, based on the coil temperature detected by the temperature sensor, to suppress iron loss and/or to prevent coil from suffering heat damage. Further, as disclosed in Japanese Patent Laid-open Publication No. 2005-86882, there is available a motor which actively cools the coil using refrigerant, such as hydraulic oil, or the like, to suppress increase of coil temperature to thereby prevent excessive heating of the rotating electric machine.
In an arrangement, like the motor disclosed in the above described Japanese Patent Laid-open Publication No. 2005-86882, in which a thermistor is provided in contact with a coil end portion to detect coil temperature, a flat thermistor contacts the wires of the coil substantially on line areas, that is, only on a small area. Therefore, if hydraulic oil as the refrigerant should flow on the surface of the thermistor, the temperature to be detected by the thermistor is significantly affected by the hydraulic oil, which is lower in temperature than the coil. As a result, coil temperature may not be accurately detected.